Lost the formatting method call in checked field getter

[bin1357]

Are you submitting a bug report or a feature request?

bug report
Lost the formatting method call in getting the checked field value
https://github.com/final-form/react-final-form/blob/master/src/useField.js#L221
it is impossible to make a checkbox that would switch between two true values. For example 'on' and 'off'

What is the current behavior?

it is impossible

What is the expected behavior?

it is possible

Sandbox Link

https://codesandbox.io/s/keen-oskar-l1vku

[bin1357]

https://codesandbox.io/s/final-formreact-final-form-simple-forked-f4j86 fixed

[bin1357]

<Field
    name="employed"
    parse={(t) => (t ? "on" : "off")}
    format={(f) => (f === "on" ? true : false)}
    component="input"
    type="checkbox"
/>

[ArturKp]

I'm not familiar with the codebase, so can't say anything about the code changes, but this seems to also fix my odd usecase, which I was expecting to work.

parse={t => t ? null : 1}
format={f => f === null}

Checked: null
Unchecked: 1

[erikras]

Published fix in v6.5.2.